1. Field of the Invention
The present invention relates to a synthetic antiferromagnetic pinned layer having a pair of ferromagnetic layers which are antiferromagnetic-coupled to each other with a nonmagnetic intermediate layer in between, a magnetoresistive device having the same, a thin film magnetic head, a head gimbals assembly, a head arm assembly, a magnetic disk apparatus, a magnetic memory cell, and a current sensor.
2. Description of the Related Art
For reading information on a magnetic recording medium such as a hard disk, a thin film magnetic head having an MR (Magneto-Resistive) device exhibiting the MR effect is widely used. In recent years, as recording density of a magnetic recording medium is becoming higher and higher, a thin film magnetic head using a giant magneto-resistive device (GMR device) exhibiting the GMR effect is commonly used. An example of the GMR device is a spin valve (SV) type GMR device.
The SV-type GMR device has an SV film obtained by stacking a magnetic layer (magnetization pinned layer) whose magnetization direction is pinned in a predetermined direction and a magnetic layer (magnetization free layer) whose magnetization direction changes according to a signal magnetic field from the outside, with a nonmagnetic intermediate layer in between. In a read operation, for example, read current flows in a stack layer in-plane direction. Such a GMR device is called, in particular, a CIP (Current in Plane)-GMR device. In this case, electric resistance (that is, voltage) changes when sense current is passed according to relative angles of the magnetization directions in the two magnetic layers (the magnetization pinned layer and the magnetization free layer) of the SV film.
Recently, a thin film magnetic head having a CPP (Current Perpendicular to the Plane)—GMR element constructed so that read current flows in a stacking direction of the SV film is being developed to address further improvement in recording density. Such a CPP-GMR element has, generally, the SV film, a pair of magnetic domain control films disposed so as to face each other while sandwiching the SV film in a direction corresponding to a read track width direction via an insulating film, and upper and lower electrodes formed so as to sandwich the SV film and the pair of magnetic domain control films in a stacking direction. The upper and lower electrodes also serve as upper and lower shield films. The CPP-GMR element having such a configuration has an advantage such that, in the case of reducing the dimension in the direction of the read track width, a higher output can be obtained as compared with a CIP-GMR element. Concretely, in the CIP-GMR element, read current is passed in the in-plane direction so that, in association with reduction in the dimension in the read track width direction, a magnetosensitive part through which the read current passes becomes smaller, and a voltage change amount decreases. On the other hand, in the CPP-GMR element, read current is passed in the stacking direction, so that the influence of reduction in the dimension in the read track width direction on the voltage change amount is small. Against such a background, expectations for the CPP-GMR element as an element which can address further improvement in recording density are rising.
In particular, in the case where the magnetization pinned layer is a synthetic layer having a three-layer structure constructed by two ferromagnetic layers (first and second ferromagnetic layers) whose magnetization directions are pinned anti-parallel to each other and a nonmagnetic intermediate layer provided between the two ferromagnetic layers, even when the net moment is reduced and an external magnetic field is applied, rotation of the magnetization direction is suppressed. Moreover, exchange coupling occurs between the two ferromagnetic layers, so that the magnetization directions are stabilized. In addition, by reduction of the net moment, static magnetic field in a magnetic head decreases, and symmetry of an output waveform is improved. A synthetic CPP-GMR element having such a synthetic magnetization pinned layer can exhibit excellent performance as means for reading magnetically recorded information because of the features of the structure.
A CPP-GMR element having a synthetic magnetization pinned layer is disclosed in, for example, Japanese Patent Laid-open No. 2005-18973 that describes a magnetoresistive sensor including a stacked ferromagnetic pinned layer constructed by sandwiching an antiferromagnetic coupling film (nonmagnetic intermediate layer) made of an alloy containing ruthenium (Ru) and iron (Fe) by two ferromagnetic layers. With the configuration, strength of exchange coupling (antiferromagnetic coupling) between the two ferromagnetic layers is increased.